Quality of service based optical network topology databases

ABSTRACT

Quality of service based optical network topology databases are described. According to one embodiment of the invention, a set of one or more connectivity constraints that include quality of service (QoS) based criteria are applied on a physical network topology of a wave length division multiplexing optical network to divide that optical network into separate service levels. In addition, service level topologies are determined for each of the service levels.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This is a continuation of application Ser. No. 10/455,933, filedJun. 6, 2003.

BACKGROUND

[0002] 1. Field

[0003] Embodiments of the invention relate to the field of networking;and more specifically, to optical networks.

[0004] 2. Background

[0005] Generalized Multiprotocol Label Switching (GMPLS) [RFC3471]extends the Multiprotocol Label Switching (MPLS) architecture [RFC3031]to encompass time-division (e.g., Synchronous Optical Network andSynchronous Digital Hierarchy, SONET/SDH), wavelength (optical lambdas)and spatial switching (e.g., incoming port or fiber to outgoing port orfiber).

[0006] GMPLS extends MPLS to include network devices whose forwardingplane recognizes neither packet, nor cell boundaries, and therefore,can't forward data based on the information carried in either packet orcell headers. Specifically, such network devices include devices wherethe forwarding decision is based on time slots (TDM), wavelengths(lambda), or physical (fiber) ports. GMPLS supports uni-directionallabel switched paths (LSPs) and bi-directional LSPs (For bi-directionalLSPs, the term “initiator” is used to refer to a node that starts theestablishment of an LSP and the term “terminator” is used to refer tothe node that is the target of the LSP; Note that for bi-directionalLSPs, there is only one “initiator” and one “terminator”) and a specialcase of Lambda switching, called Waveband switching (A wavebandrepresents a set of contiguous wavelengths which can be switchedtogether to a new waveband; The Waveband Label is defined to supportthis special case; Waveband switching naturally introduces another levelof label hierarchy; As far as the MPLS protocols are concerned there islittle difference between a waveband label and a wavelength label.).

[0007] To deal with the widening scope of MPLS into the optical and timedomain, there are several new forms of “label.” These new forms of labelare collectively referred to as a “generalized label.” A generalizedlabel contains enough information to allow the receiving node to programits cross connect, regardless of the type of this cross connect, suchthat the ingress segments of the path are properly joined. TheGeneralized Label extends the traditional label by allowing therepresentation of not only labels which travel in-band with associateddata packets, but also labels which identify time-slots, wavelengths, orspace division multiplexed positions. For example, the Generalized Labelmay carry a label that represents (a) a single fiber in a bundle, (b) asingle waveband within fiber, (c) a single wavelength within a waveband(or fiber), or (d) a set of time-slots within a wavelength (or fiber).It may also carry a label that represents a generic MPLS label, a FrameRelay label, or an ATM label (VCI/VPI).

[0008] Thus, GMPLS forms label switched paths (LSPs) through thenetwork. These paths may be connection oriented or connectionless. Forinstance, the Resource Reservation Protocol (RSVP) is often used todeploy connection oriented LSPs, whereas a label management protocol(LMP), such as the label distribution protocol (LDP), is often used toprovision connectionless LSPs.

[0009] Optical Networks

[0010] An optical network is a collection of optical network devicesinterconnected by links made up of optical fibers. Thus, an opticalnetwork is a network in which the physical layer technology isfiber-optic cable. Cable trunks are interconnected with opticalcross-connects (OXCs), and signals are added and dropped at opticaladd/drop multiplexers (OADMs). The optical network devices that allowtraffic to enter and/or exit the optical network are referred to asaccess nodes; in contrast, any optical network devices that do not arereferred to as pass-thru nodes (an optical network need not have anypass-thru nodes). Each optical link interconnects two optical networkdevices and typically includes an optical fiber to carry traffic in bothdirections. There may be multiple optical links between two opticalnetwork devices.

[0011] A given fiber can carry multiple communication channelssimultaneously through a technique called wavelength divisionmultiplexing (WDM), which is a form of frequency division multiplexing(FDM). When implementing WDM, each of multiple carrier wavelengths (or,equivalently, frequencies or colors) is used to provide a communicationchannel. Thus, a single fiber looks like multiple virtual fibers, witheach virtual fiber carrying a different data stream. Each of these datastreams may be a single data stream, or may be a time division multiplex(TDM) data stream. Each of the wavelengths used for these channels isoften referred to as a lamda.

[0012] A lightpath is a one-way path in an optical network for which thelamda does not change. For a given lightpath, the optical nodes at whichits path begins and ends are respectively called the source node and thedestination node; the nodes (if any) on the lightpath in-between thesource and destination nodes are called intermediate nodes. An opticalcircuit is a bi-directional, end to end (between the access nodesproviding the ingress to and egress from the optical network for thetraffic carried by that optical circuit) path through the opticalnetwork. Each of the two directions of an optical circuit is made up ofone or more lightpaths. Specifically, when a given direction of the endto end path of an optical circuit will use a single wavelength, then asingle end to end lightpath is provisioned for that direction (thesource and destination nodes of that lightpath are access nodes of theoptical network and are the same as the ends nodes of the opticalcircuit). However, in the case where a single wavelength for a givendirection will not be used, wavelength conversion is necessary and twoor more lightpaths are provisioned for that direction of the end to endpath of the optical circuit. Thus, a lightpath comprises a lamda and apath (the set of optical nodes through which traffic is carried withthat lambda).

[0013] Put another way, when using GMPLS on an optical network, theoptical network can be thought of as circuit switched, where LSPs arethe circuits. Each of these LSPs (unidirectional or bi-directional)forms an end to end path where the generalized label(s) are thewavelength(s) of the lightpath(s) used. When wavelength conversion isnot used for a given bi-directional LSP, there will be a single end toend lightpath in each direction (and thus, a single wavelength; andthus, a single generalized label).

[0014] An optical network device can be thought of comprising 2 planes:a data plane and a control plane. The data plane includes thosecomponents through which the light travels (e.g., the switch fabric oroptical crossconnect; the input and output ports; amplifiers; buffers;wavelength splitters or optical line terminals; adjustable amplifiers;etc.), add/drop components (e.g., transponder banks or optical add/dropmultiplexers, etc.), and components that monitor the light. The controlplane includes those components that control the components of the dataplane. For instance, the control plane is often made up softwareexecuting on a set of one or more microprocessors inside the opticalnetwork device which control the components of the data plane. Toprovide a specific example, the software executing on themicroprocessor(s) may determine that a change in the switch fabric isnecessary, and then instruct the data plane to cause that switch tooccur. It should also be noted that the control plane of an opticalnetwork device is in communication with a centralized network managementserver and/or the control planes of one or more other network devices.

[0015] A number of different network topologies have been developed foroptical network devices, including ring and meshed based topologies.Similarly, a number of different control planes and data planes havebeen developed for optical network devices. For instance, wavelengthdivision multiplexing (WDM) necessitated an alteration of the data planeand the control plane. As another example, various different techniqueshave been used for implementing the switch fabric, including opticalcross connects such as MEMS, acousto optics, thermo optics, holographic,and optical phased array.

[0016] Operating an optical network typically requires: A) building andmaintaining network databases; and B) establishing lightpaths. Forexample, the network databases can include: 1) link state databases thattrack information (e.g., the link(s), lamda(s), lamda bandwidths, etc.)regarding adjacent optical nodes (e.g., using a link management protocol(LMP)); and 2) topology databases that track information (e.g., nodes,links, lamdas, etc.) for the physical connectivity of the nodes in adomain and/or the entire network (e.g., using OSPF-TE). In order toestablish an LSP, the following operations are typically performedoffline: 1) determining the shortest path(s) between source anddestination using a shortest path first algorithm based on the networkdatabase(s); 2) determining the wavelength(s) available on theseshortest path(s) based on the network database(s); 3) allocate awavelength from the available wavelengths on the shortest path (oftenreferred to as signaling the path; effectively telling the involvedoptical network devices how to configure their switch fabrics; e.g.,using RSVP or CR-LDP based signaling with GMPLS). Steps 1 and 2 can bereversed.

[0017] There are generally three approaches to operating an opticalnetwork: 1) centralized static provisioning; 2) source based staticprovisioning; and 3) hybrid static provisioning. In centralized staticprovisioning, a separate centralized network management server maintainsa network topology database and communicates with each of the opticalnetwork devices of a network. In response to some predefined demands foran optical circuit, the network management server finds the shortestpath(s) and selects a wavelength(s) on one. The network managementserver then causes the allocation of the wavelength(s) and theconfiguring of the switch fabrics.

[0018] In source based static provisioning, each of the access nodes ofthe network performs the work of building/maintaining a network topologydatabase. In response to some predefined demands for an optical circuitreceived by an access node, that node: 1) buffers the traffic asnecessary; 2) finds the shortest path(s) and selects a wavelength(s) onone; and 3) causes the allocation of the wavelength and the configuringof the switch fabrics.

[0019] In hybrid static provisioning, each of the nodes of the networkuse OSPF-TE to build network topology databases, and from there anetwork topology database is built and maintained in a centralizednetwork management server. The network management server initiates aform of source based provisioning. This allows a network administratorto maintain control over provisioning of each lightpath provisioned.

[0020] One problem with existing optical networks is the networktopology databases used and the manner in which they are built andmaintained. Specifically, these monolithic physical topology databases(e.g., built with OSPF-TE) are very large because they must store all ofthe data to give a physical view of the network (not only connectivityat the link level, but connectivity at the lamda level because there aremultiple lamdas per link and because different lamdas on a given linkmay provide different bandwidths; etc.). These large network databasesare relatively time consuming to parse and require a relatively longtime and a relatively large amount of node intercommunication topropagate changes. In addition, such network topology databases wouldbecome even larger if QoS type information needed to be recorded.

[0021] Another problem with existing optical network devices is therestatic, off-line nature of operation (e.g., using centralized staticprovisioning, source based static provisioning, hybrid staticprovisioning, etc.). More particularly, based upon a determination ofthe projected needs of the end node to end node connection through theoptical network and the then existing state of the optical network(basically, a snapshot of the network parameters), an optical circuit isprovisioned through the optical network over which the traffic is totravel. This optical circuit will be static in the sense that it willnot be altered on the fly based upon current bandwidth requirements(demand changes), current status of the network, etc. Instead, thisoptical circuit will only be modified when it is re-provisioned (e.g.,at the request of the customer to upgrade to a larger or smaller amountof bandwidth) and/or some form of protection switch based on aredundancy scheme.

[0022] Therefore, a given optical circuit is established at the maximumbandwidth believed to be required at any given point in time, and thismaximum bandwidth is provisioned for that purpose. That is to say, agiven customer is provisioned a fixed amount of bandwidth for allclasses of traffic, whether that customer at any given point in time isusing some, all or none of that bandwidth. Due to variations in thebandwidth requirements and/or the status of the network, bandwidth willgo unused.

[0023] Thus, the optical layer is operated to provide point-to-pointlinks, with no intelligence and no real time decision-makingcapabilities. In addition, the need for demands to be known in advanceimposes difficulties for service creation and service provisioning. Thisresults in an inefficient utilization of resources at the optical layer.

[0024] Furthermore, while there has been work to provide quality ofservice (QoS) at the IP layer and/or using MPLS, both of these protocolsare carried over SONET; where SONET does not distinguish the types oftraffic (does, not provide QoS). Thus, typical optical control planes dono provide the ability to separate traffic into different classes basedon service level requirements (i.e., they do not incorporate servicelevel requirements of different types of traffic in lightpathcalculations).

[0025] In addition, redundancy is maintained in typical optical networksusing either: 1) 1+1 protected lightpaths; 2) 1:1 protected lightpaths;or 3) mesh restored lightpaths. A 1+1 protected lightpath from node A tonode B is a pair of node diverse paths in the network where one of thepaths is a working path, and the other is a protection path. The workingpath and the protection path are established at the same time; when afailure occurs over the working path, traffic is switched to theprotection path. A mesh restored lightpath from node A to node B is apair of shared resource group disjoint paths in the network, where oneof the routes is a working path and the other is a backup path. Thecapacity dedicated on the backup path can be shared with backup paths ofother mesh-restored lightpaths. Existing optical networks use one or theother of these redundancy schemes irrespective of the criticality of thedata.

BRIEF SUMMARY

[0026] Quality of service based optical network topology databases aredescribed. According to one embodiment of the invention, a set of one ormore connectivity constraints that include quality of service (QoS)based criteria are applied on a physical network topology of a wavelength division multiplexing optical network to divide that opticalnetwork into separate service levels. In addition, service leveltopologies are determined for each of the service levels.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention may best be understood by referring to thefollowing description and accompanying drawings that are used toillustrate embodiments of the invention. In the drawings:

[0028]FIG. 1 is a block diagram illustrating an exemplary opticalnetwork according to one embodiment of the invention.

[0029]FIG. 2 is a block diagram illustrating exemplary QoS based logicalnetwork views of the exemplary optical network of FIG. 1 according tocertain embodiments of the invention.

[0030]FIG. 3A illustrates service level A's conversion free servicelevel topology for N1 of the optical network in FIG. 2 according tocertain embodiments of the invention.

[0031]FIG. 3B illustrates service level B's conversion free servicelevel topology for N1 of the optical network in FIG. 2 according tocertain embodiments of the invention.

[0032]FIG. 3C illustrates service level C's conversion free servicelevel topology for N1 of the optical network in FIG. 2 according tocertain embodiments of the invention.

[0033]FIG. 4 is a block diagram illustrating a hierarchy of termsaccording to certain embodiments of the invention.

[0034]FIG. 5 is a flow diagram for building and maintaining networktopology databases with a set of connectivity constraints according tocertain embodiments of the invention.

[0035]FIG. 6 is a flow diagram illustrating the provisioning oflightpaths according to certain embodiments of the invention.

[0036]FIG. 7 is a block diagram illustrating an exemplary access nodeaccording to certain embodiments of the invention.

[0037]FIG. 8 is an exemplary data flow diagram of a distributed searchbased technique's formation of service level A's service level topologyfor N1 of the optical network in FIG. 2 according certain embodiments ofthe invention.

[0038]FIG. 9 is a flow diagram performed by each access node whenjoining an optical network according to embodiments of the invention.

[0039]FIG. 10 is a flow diagram illustrating a service level topologybuild-up for a single service level according to embodiments of theinvention.

[0040]FIG. 11 is a flow diagram illustrating operations performed bynodes responsive to a connectivity request message received over a linkaccording to certain embodiments of the invention.

[0041]FIG. 12 is the flow diagram illustrating operations performed byan access node to allocate a path according to certain embodiments ofthe invention.

[0042]FIG. 13 is a flow diagram illustrating operations performed by anaccess node responsive to an update routing database message accordingto certain embodiments of the invention.

[0043]FIG. 14 is a flow diagram illustrating operations performed by anaccess node responsive to an update allocate channel message accordingto certain embodiments of the invention.

[0044]FIG. 15 is a flow diagram illustrating operations performed by thesource node of a path responsive to that path being deallocatedaccording to certain embodiments of the invention.

[0045]FIG. 16 is a flow diagram illustrating operations performed byaccess nodes responsive to an update deallocate channel messageaccording to certain embodiments of the invention.

[0046]FIG. 17 is a flow diagram illustrating the operations performed bythe access nodes connected by the link on which the channel isadded/removed according to certain embodiments of the invention.

[0047]FIG. 18 is a flow diagram illustrating the operations performed byan access node responsive to receiving an update add/remove channelmessage according to certain embodiments of the invention.

[0048]FIG. 19 is a flow diagram illustrating the operations performed bythe access nodes connected by the removed link according to certainembodiments of the invention.

[0049]FIG. 20 is a flow diagram illustrating the operations performed byan access node responsive to receiving a link removal message accordingto certain embodiments of the invention.

[0050]FIG. 21 is a flow diagram illustrating the operations performed bythe access nodes connected by the added link according to certainembodiments of the invention.

[0051]FIG. 22 is a flow diagram illustrating the operations performed byan access node responsive to receiving a link addition message accordingto certain embodiments of the invention.

[0052]FIG. 23 is a flow diagram illustrating the operations performed bythe access node(s) adjacent a removed node according to certainembodiments of the invention.

[0053]FIG. 24 is a flow diagram illustrating the operations performed byan access node responsive to receiving a node removal message accordingto certain embodiments of the invention.

[0054]FIG. 25 is a flow diagram illustrating the operations performed byan access node responsive to receiving a node addition message accordingto certain embodiments of the invention.

DETAILED DESCRIPTION

[0055] In the following description, numerous specific details are setforth (e.g., such as logic resource partitioning/sharing/duplicationimplementations, types and interrelationships of system components, andlogic partitioning/integration choices). However, it is understood thatembodiments of the invention may be practiced without these specificdetails. In other instances, well-known circuits, software instructionsequences, structures and techniques have not been shown in detail inorder not to obscure the understanding of this description.

[0056] References in the specification to “one embodiment”, “anembodiment”, “an example embodiment”, etc., indicate that the embodimentdescribed may include a particular feature, structure, orcharacteristic, but every embodiment may not necessarily include theparticular feature, structure, or characteristic. Moreover, such phrasesare not necessarily referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with an embodiment, it is submitted that it is within theknowledge of one skilled in the art to effect such feature, structure,or characteristic in connection with other embodiments whether or notexplicitly described.

[0057] In the following description and claims, the terms “coupled” and“connected,” along with their derivatives, may be used. It should beunderstood that these terms are not intended as synonyms for each other.Rather, in particular embodiments, “connected” may be used to indicatethat two or more elements are in direct physical or electrical contactwith each other. “Coupled” may mean that two or more elements are indirect physical or electrical contact. However, “coupled” may also meanthat two or more elements are not in direct contact with each other, butyet still co-operate or interact with each other.

[0058] Overview

[0059] According to embodiments of the invention, a set of one or moreconnectivity constraints is imposed on the building/maintaining ofnetwork topology databases. As a result of the set of connectivityconstraints, such network topology databases are smaller in comparisonto network topology databases that represent all physical connectivityin the network. According to one aspect of the invention, the set of oneor more connectivity constraints includes one or more QoS basedcriteria; thus, effectively dividing the optical network into QoS basedlogical network views that may be used to provision differentwavelengths for different classes of traffic based on differing QoSrequirements. According to another aspect of the invention, the set ofone or more connectivity constraints includes a conversion freeconstraint; this allows for establishing conversion free opticalcircuits. According to another aspect of the invention, a distributedsearch based technique is used for building and maintaining networktopology databases based on a set of connectivity constraints. Accordingto another aspect of the invention, an optical network uses a sourcebased scheme in which network topology databases, based on a set ofconnectivity constraints, are kept in access nodes. The reduced networktopology database size (as compared to a physical network topologydatabase) and distributed nature of this source based scheme allows forthe provisioning of optical circuits in real-time (or on the fly; thatis, the demands do not need to know ahead of time).

[0060] Since each of the above aspects is independent, differentembodiments may implement different ones and/or combinations of theabove aspects of the invention. For example, certain embodiments of theinvention include in the set of connectivity constraints both QoScriteria and conversion free constraints. The network topology databasesbased on this set of connectivity constraints: 1) have reduced size overfull physical connectivity network topology databases; 2) allowdifferent traffic to be given different wavelengths based on QoS fordifferent classes of traffic; and 3) allow for establishing conversionfree optical circuits. While certain of these embodiments implementsource based schemes and build/maintain the network topology databasesusing a distributed search based technique, others of these embodimentsmay use a different scheme and/or a different databasebuilding/maintaining technique.

EXEMPLARY QoS EMBODIMENTS

[0061] Different embodiments of the invention may support different QoScriteria. For example, the QoS critera may include bandwidth, bit errorrate, optical signal to noise ratio, peak noise level, re-routingpriority, etc. In other words, the QoS criteria may include any criteriathat allows different wavelengths to be distinguished from each otherbased on quality of service. For a given wavelength on a given link, thevalues for the QoS criteria (the wavelength parameters) may bedetermined based on the configuration (e.g., the type of laser used)and/or by monitoring the light.

[0062] The QoS criteria is used to classify wavelengths on links intoone of the set of supported service levels. In particular, for each ofthe QoS criteria, there is a service level parameter provided for eachservice level. The wavelength parameters of a given wavelength on agiven link are compared against the service level parameters to classifythat wavelength into one of the service levels.

[0063] Exemplary Network

[0064] In certain optical networks, different wavelengths in at leastcertain nodes have different wavelength parameters. For instance, agiven optical network device may have different groups of wavelengthsimplemented to operate at different bandwidths (e.g., group A at OS-X,group B at OS-Y, and group C at OS-Z) and service level parameters thatdistinguish based on bandwidth. As a result, the optical network notonly has a given interconnectivity at the physical link level (aphysical topology), but also has a given interconnectivity for eachservice level (for each service level, a service level topology for thenetwork and for each node), and a given interconnectivity for eachconversion free service level (for each service level, a conversion freeservice level topology for each node).

[0065]FIG. 1 is a block diagram illustrating an exemplary opticalnetwork according to one embodiment of the invention. The opticalnetwork of FIG. 1 includes 5 access nodes labeled N1, N2, N3, N4, andN5. The ability to implement multiple lamdas on a single link isrepresented in simplified form by numbering the lamdas; lamdas havingthe same number are the same wavelength. FIG. 1 shows the numberedlamdas available on each optical link of the exemplary optical network.The term “available” when used in conjunction with a lamda numberindicates that the node is capable of producing that wavelength; theterms allocated and unallocated are used to identify whether or not thatavailable wavelength is currently provisioned. To describe the physicalconnectivity illustrated in FIG. 1, the format of node number: nodenumber is used to indicate there is an optical link between those nodes;and node number: node number equals lamda number(s) indicates thewavelengths available on that link. Using this format, FIG. 1 shows:N2:N2=lamda 1, 2, 3, 4; N2:N4=lamda 1, 3, 5; N4:N5:=lamda 1, 2, 3, 4;N1:N3=lamda 1, 2, 4; and N3:N4=lamda 1, 2, 4.

[0066] It should be understood that the topology in FIG. 1 is exemplary,and that the invention can be used with any number of differenttopologies. In addition, while FIG. 1 illustrates different wavelengthsbeing available on different optical links, it is understood that thesame wavelengths may be available on all of the optical links.Furthermore, while specific wavelengths are identified as beingavailable in FIG. 1, optical network devices may be implemented withlasers to allow them to generate a variety of different wavelengths andthe invention is equally applicable to optical networks containing oneor more such optical network devices. However, for purposes ofillustration, embodiments of the invention will be described withreference to the wavelengths illustrated in FIG. 1. While the exemplaryoptical network in FIG. 1 is made up of access nodes, embodiments of theinvention are equally applicable to optical networks that include passthrough nodes.

[0067]FIG. 2 is a block diagram illustrating exemplary QoS based logicalnetwork views of the exemplary optical network of FIG. 1 according tocertain embodiments of the invention. In the example of FIG. 2, the setof supported service levels includes service levels A, B, and C. Thewavelength parameters of each wavelength on each link have been comparedagainst the service level parameters to classify each wavelength on eachlink into one of the service levels A, B, and C. To refer to a givenservice level, an S is placed in front of the service level label (SA,SB, SC). The format for identifying the wavelengths on a given linkclassified to a given service level is best provided by example.Specifically, SA (N1:N2)=lamda 1, 2 indicates that there is an opticallink between N1 and N2, and that the wavelength parameters of lamda 1and lamda 2 on that link qualify them for service level A (lamda 1 and 2are referred to as the link service level channel set on link N1:N2 forservice level A). Using this format, FIG. 2 illustrates the connectivityof service level A being: SA (N1:N2)=lamda 1, 2; SA (N2:N4)=lamda 1; SA(N4:N5)=lamda 1, 2; SA (N1:N3)=lamda 1, 2; SA (N3:N4)=lamda 1, 2. Theservice level connectivity for service level B is SB (N1:N2)=lamda 3; SB(N2:N4)=lamda 3; SB (N4:N5)=lamda 3; SB (N1:N3)=X; and SB (N3:N4)=X(where X indicates a null set). The connectivity of service level C is:SC (N1:N2)=lamda 4; SC (N2:N4)=lamda 5; SC (N4:N5)=lamda 4; SC(N1:N3)=lamda 4; and SC (N3:N4)=lamda 4.

[0068] Thus, while FIG. 1 illustrates the connectivity at the physicallink level, FIG. 2 illustrates the connectivity for each service level(a service level topology for the network). Effectively, this servicelevel node connectivity divides the optical network into QoS basedlogical network views as illustrated. Thus, for a first access nodethere are one or more paths across physical links to a second accessnode (physical topology). For any given one of these paths, there maybe, on each of the link(s) making up that path, wavelengths at the sameservice level. For any given one of these paths, there may also be, onthe link(s) making up that path, one or more of the same wavelengths atthe same service level.

[0069] FIGS. 3A-C illustrate the conversion free service leveltopologies for service levels A-C for N1 of the optical network in FIG.2 according to certain embodiments of the invention. Specifically, FIGS.3A-C illustrate conversion free service level topologies in the form oftrees having N1 as the root with branches representing links from nodeto node through the network. As used below, the phrase “path servicelevel channel set” refers to the intersection set of the link servicelevel channel sets on the links of the path. For example, the pathservice level channel set for the path N1:N2:N4:N5 at service level A isthe intersection set of the link service level channel sets SA (N1:N2),SA (N2:N4), and SA (N4:N5).

[0070]FIG. 3A illustrates service level A's conversion free servicelevel topology for N1 of the optical network in FIG. 2 according tocertain embodiments of the invention. In FIG. 3A, N1 has branches to N2and N3. With regard to the branch to N2, both lamda 1 and lamda 2 areavailable at service level A. Thus, for the path from N1 to N2, lamda 1and lamda 2 make up the path service level channel set for service levelA. Similarly, for the branch from N1 to N3, the path service levelchannel set includes lamda 1 and 2. It should be noted that for pathsbetween adjacent nodes, the link service level channel set (e.g.,SA(N1:N2)=lamda 1,2) is the same as the path service level channel set.

[0071] From each of N2 and N3, there is a branch to a differentrepresentation of N4. The branch from N2 to N4 represents the pathN1:N2:N4. Since the link service level channel sets for N1:N2 and forN2:N4 respectively include lamda 1,2 and lamda 2, the intersection ofthese link service level channel sets includes only lamda 1 (the onlyconversion free N1:N2:N4 path uses lamda 1 on both N1:N2 and N2:N4). Assuch, the path service level channel set for the path N1:N2:N4 includesonly lamda 1. In contrast, the branch from N3 to N4 represents the pathN1:N3:N4. Since the intersection of the link service level channel setsfor N1:N3 and N3:N4 includes lamda 1 and 2, the path service levelchannel set for the path N1:N3:N4 includes lamda 1 and 2.

[0072] The branch from N1 to N4, through N2, branches to: 1) N3 withpath service level channel set lamda 1; and 2) N5 with path servicelevel channel set lamda 1. The branch from N1 to N4, through N3,branches to: 1) N2 with path service channel set lamda 1; and 2) N5 withpath service level channel set lamda 1, 2. It should be noted that eventhough the link service level channel set for N4:N5 includes lamda 1,2,the path service level channel set for N1:N2:N4:N5 includes only lamda 1to remain conversion free. This is in contrast to the path service levelchannel set for N1:N3:N4:N5 which includes both lamda 1 and 2 becauseboth are available on each link of this path.

[0073]FIG. 3B illustrates service level B's conversion free servicelevel topology for N1 of the optical network in FIG. 2 according tocertain embodiments of the invention. Since there is no lamda thatqualifies for service level B on the link N1:N3, the tree of FIG. 3Bdoes not have a branch from N1 to N3. However, there is a branch from N1to N2, and the path service level channel set for the branch from N1 toN2 includes lamda 3. N2 has a branch to N4, which branch has as its pathservice level channel set lamda 3. Since there is no lamda qualifyingfor service level B on the link from N4 to N3, there is not a branchfrom N4 to N3. However, there is a branch to N5, and the path servicelevel channel set for N1:N3:N4:N5 includes lamda 3.

[0074]FIG. 3C illustrates service level C's conversion free servicelevel topology for N1 of the optical network in FIG. 2 according tocertain embodiments of the invention. The tree of FIG. 3C has branchesfrom N1 to: 1) N2 with path service level channel set lamda 4; and 2) N3with path service level channel set lamba 4. There is no branch from N2because wavelength conversion would be necessary (the link service levelchannel set for N2:N4 is lamda 5, whereas the path service level channelset for the path from N1 to N2 includes lamda 4). There is a branch fromN3 to N4, which branch has as its path service level channel set lamda4. There are branches from N4 to each of N2 and N5, both of which thepath service level channel set includes lamda 4.

[0075] It should be understood that a given topology for a node may beservice level based and/or conversion free based (depending on the setof connectivity constraints used). Thus, the phrase “service leveltopology” for a node indicates that at least a QoS based criteria isused, but it does not exclude the use of conversion free criteria(except where otherwise indicated herein); likewise, the phrase“conversion free topology” for a node indicates that at least aconversion free criteria is used, but it does no exclude the use of aQoS based criteria (except where otherwise indicated herein). In otherwords, to say a topology for a node is service level based does notindicate whether or not it is also conversion free based; to say atopology for a node is conversion free based does not indicate whetheror not it is also service level based; but to say a topology for a nodeis conversion free based and QoS based indicates it must be both.

[0076] It should also be understood that if the set of connectivity,constraints includes QoS based criteria, then there are service leveltopologies for the network and service level topologies (or conversionfree service level topologies if a conversion free criteria is alsoused) for each node; if the set of connectivity constraints includes aconversion free criteria, then there is a conversion free topology (or aconversion free service level topology if QoS based criteria are alsoused) for each node. Different embodiments may store network topologydatabases that represent one or more of these different topologies indifferent devices depending on the implementation and the set ofconnectivity constraints used. For example, a centralized networkmanagement server may store network topology database(s) representing:service level topologies for the network, service level topologies foreach node, one or more conversion free topologies for each node, and/orconversion free service level topologies for each node. As anotherexample, each access node may store may store network topologydatabase(s) representing: service level topologies for the network,service level topologies for that node, one or more conversion freetopologies for that node, and/or conversion free service leveltopologies for that node. It should be understood that otherconfigurations are within the scope of the invention.

[0077]FIG. 4 is a block diagram illustrating a hierarchy of termsaccording to certain embodiments of the invention. The terms illustratedin FIG. 4 will be used with respect to certain embodiments of theinvention described below. With reference to FIG. 4, the network isdivided into a set of one or more service levels, each service levelincludes a set of zero or more possible end to end paths, each of thesepossible end to end paths includes a set of one or more links, and eachlink includes one or more available lamdas. The possible end to endpaths of a given service level are referred to as the set of possibleend to end service level paths (all paths that can be made betweenaccess nodes with the available lamdas at that service level). The unionof the possible end to end service level paths of all the service levelsis referred to as the set of possible end to end network paths. Thelinks making up a given path are referred to as the set of path links,whereas the union of the links of all the possible end to end paths in aset of possible end to end service level paths is referred to as the setof service level links. The lamdas on a link of a possible end to endpath of a service level are referred to as the link lamdas, whereas theunion of the lamdas on the links of a possible end to end path of aservice level are referred to as the path lamdas. The term service levellink lamdas is used to refer to the links of the service level links andthe lambas thereon qualifying for that service level.

[0078] The hierarchy illustrated in FIG. 4 provides a framework for theset of connectivity constraints including one or more QoS based criteriathat divide the network into service levels. When the set of one or moreconnectivity constraints also includes a conversion free constraint, thelink lamdas of the links of a possible end to end path of a servicelevel will all be the same. In other words, to provide a conversion freeend to end path, the same lamda must be used on each link of the end toend path (that lamda must qualify for the same service level on eachlink of the path). In contrast, when the set of connectivity constraintsdoes not include a conversion free constraint, the set of link lamdasmay be different for different links of a possible end to end path of aservice level.

[0079] Building and Maintaining Network Topology Databases with a Set ofConnectivity Constraints

[0080] While various techniques are described with reference to thebuilding and maintaining of network topology databases with a set ofconnectivity constraints, it is understood that this is an aspect of theinvention independent of other aspects of the invention; thus, theinvention is not limited to the exemplary techniques of building andmaintaining network topology databases with a set of connectivityconstraints as described herein.

[0081] Overview

[0082]FIG. 5 is a flow diagram for building and maintaining networktopology databases with a set of connectivity constraints according tocertain embodiments of the invention. It should be understood thatdifferent ones of the blocks in FIG. 5 could be performed in adistributed and/or centralized manner as described in more detail below.

[0083] In block 505, the lamdas for each link are tracked and controlpasses to block 505. While certain embodiments of the invention use alink management protocol (LMP) to discover the adjacent links betweennodes, alternative embodiments of the inventions may use othertechniques (e.g., a manual input technique into each node, a manualinput technique into a centralized network management server, etc.). Inaddition, while certain embodiments of the invention include amonitoring unit in one or more nodes of the network to measurewavelength parameters, alternative embodiments of the invention can useother techniques (e.g., periodic external testing devices, manual inputinto to each node of wavelength parameters, manual input of wavelengthparameters into a centralized network management server, etc.).

[0084] As shown in block 510, a classification by QoS criteria ismaintained for the lamdas of each link to determine the service levellink lamdas and control flows to block 515. While in certain embodimentsblock 510 is performed by each node for its adjacent links, alternativeembodiments of the invention use an alternative technique (e.g., acentralized network management server performs block 510 responsive toreceiving wavelength parameter information as discussed with referenceto block 505).

[0085] In block 515, the service level connectivity based on theconversion criteria is maintained for each service level. The servicelevel connectivity that is maintained would include the available lamdasand the status as either allocated or unallocated. While in certainembodiments of the invention, the service level connectivity is built indistributed fashion and maintained in the access nodes, alternativeembodiments of the invention use alternative techniques (e.g., performsuch in a centralized network management server). The conversioncriteria represents the number of wavelength conversions allowable for agiven optical circuit. For example, if one of the connectivityconstraints is a conversion free connectivity constraint, the number ofwavelength conversions allowable is zero.

[0086]FIG. 6 is a flow diagram illustrating the provisioning oflightpaths according to certain embodiments of the invention. Differentembodiments of the invention may implement such provisioning using asource based, centralized, hybrid, or other provisioning scheme.

[0087] In block 605, demand criteria is received. This demand criteriarepresents a request for a communication path (e.g., an optical circuit,a lightpath, a end-to-end unidirectional path, etc.). From block 605,control passes to block 610. In certain embodiments of the inventionusing a source based scheme, the demand criteria is received by anaccess node in the optical network. In other embodiments of theinvention using a centralized network management server, such demandsare received by the network management server directly from therequester and/or from an access node in the optical network receivingthe demand criteria. Of course, alternative embodiments of the inventioncan use other schemes and/or implement the schemes in other ways.

[0088] As shown in block 610, the service level is determined if it wasnot specified and control passes to block 615. For instance, whilecertain demand requests may come from entities aware of the servicelevels provided by the optical network, other entities making requestsmay not. These later entities may either not include any parameters orinclude parameters from which a service level can be determined.

[0089] In block 615, it is determined if there is an end to end pathavailable at the determined service level. If there is a path available,control passes to block 620. Otherwise, control passes to block 625.

[0090] In block 620, a path and necessary lamda(s) are selected andallocated. The number of different wavelengths allocated will dependupon the wavelength conversion criteria (e.g., where a conversion freeconnectivity constraint is used, the same wavelength(s) will be usedacross each link of the selected path). Since this allocation affectsthe service level connectivity of block 515, block 515 is updated (e.g.,some action is taken responsive to the allocation, periodic checks ofthe formed, etc.). In certain embodiments of the invention using asource based scheme, the source node performs block 620 by: 1) selectingthe path and lamda(s); and 2) communicating with the other nodes of theoptical network to allocate. In other embodiments of the invention inwhich a centralized network management server is used, block 620 isperformed by a network management server performing the selection andcommunicating the allocation to the nodes on the path. Of course,alternative embodiments of the invention could implement other schemesin other ways.

[0091] In block 625, alternative action is taken depending upon themanner in which the optical network is administered. For instance, oneor more of the following may be options: using a path from a higherservice level, muxing two or more paths from lower service levels,allocating a single path from a lower service level, denying, allowingfor an increased amount of wavelength conversions to occur, etc.

[0092] In addition to the need to allocate responsive to demandcriteria, other operations are performed as part of administration ofthe optical network (e.g., deallocation, addition of a new wavelength,addition of a new link, failure/restoration of a wavelength,failure/restoration of a link, failure/restoration of a node, etc.). Oneor more blocks of FIG. 5 are updated responsive to these changes inorder to provide for a current view the optical network. For instance,if a request was made to deallocate a path, the node that initiated theallocation (source) is instructed to deallocate the path and block 515updates the service level connectivity of the service level, includingthe path that was deallocated. The addition of a wavelength, link ornode (as well as the removal of a wavelength, link, or a node which wascarrying no live traffic) results in an updating through blocks 505, 510and 515. The loss of a wavelength, link or node is treated as a failureupon which some action is taken depending upon the redundancy schemebeing implemented (different embodiments of the invention can usedifferent redundancy schemes) or an elimination of that wavelength, linkor node from the network.

[0093] It should also be noted that a request to change the demandcriteria for a given provisioned service (e.g., a request to lower orraise the service level of a given provisioned service) is alsoaddressed by certain embodiments of the invention. In particular,certain such embodiments respond to such requests by allocating a newpath, and if successful and necessary, moving the traffic from the oldpath to the new allocated path and deallocating the old path. Whiledifferent embodiments can perform the above using of variety ofdifferent techniques, embodiments using a source based scheme arediscussed by way of example, and not by limitation, below.

[0094] Of course, one or more parts of an embodiment of the inventionmay be implemented using any combination of software, firmware, and/orhardware. Such software and/or firmware can be store and communicated(internally and with other access nodes over the network) usingmachine-readable media, such as magnetic disks; optical disks; randomaccess memory; read only memory; flash memory devices; electrical,optical, acoustical or other form of propagated signals (e.g., carrierwaves, infrared signals, digital signals, etc.); etc.

[0095] Exemplary Distributed Search Technique

[0096] Certain embodiments of the invention will now be described withreference to a distributed search based technique for building andmaintaining in source nodes network topology databases based on a set ofconnectivity constraints that includes QoS criteria and conversion freeconstraints. However, it should be understood that alternativeembodiments may use a distributed technique, but not build and maintainthe service level topology databases in the source nodes (e.g., they maybe built and maintained in a centralized network management server). Inaddition, while a distributed search based technique is described,alternative embodiments can use alternative techniques (e.g., acentralized technique). Similarly, alternative embodiments of theinvention may not include the conversion free connectivity constraint,or relax it when necessary (e.g., when there is no conversion free endto end path at the requested service level).

[0097]FIG. 7 is a block diagram illustrating an exemplary access nodeaccording to certain embodiments of the invention. FIG. 7 shows acontrol plane 700 coupled with a data plane 701. The control plane 701includes node databases 702 coupled with node modules 735. Of course,the control plane 700 includes other items (e.g., protocols).

[0098]FIG. 7 shows the node databases 702 include a service levelconnectivity database 705, a service level parameter database 710, alink state database 715, and a routing database 720. The link statedatabase 715 includes a set of one or more link state structures 725,one for each link connected to that node. While in certain embodimentsthese links are discovered through a link management protocol,alternative embodiments could use other techniques as described above.Each link state structure records a neighboring node, a port throughwhich that neighboring node is connected (fiber links end up at a porton the node), available wavelengths on that link (through the port), aswell as each wavelength's parameters.

[0099] The service level parameter database 710 stores the service levelparameters previously discussed herein. The service level connectivitydatabase includes a set of one or more service level topology structures730, one for each service level. Each of these service level topologystructures stores a representation of the conversion free service leveltopology for that node (e.g., see FIGS. 3A-C). In addition, the servicelevel topology structure for each service level would track theallocated/unallocated status for each lamda in its topology. The statusmay not be limited to being allocated or unallocated. For example, alamba that has failed due to a fiber cut, could be assigned a status of“broken”. For embodiments in which only bi-directional paths can beallocated, the granularity for tracking allocated/unallocated status issimply the lamda level. However, in embodiments that allow forunidirectional path allocation, the granularity of allocated/unallocatedstatus is a status for each direction for each lamda.

[0100] The node modules 735 includes a start up module 740, aconnectivity request module 745, an allocate module 750, a Deallocatemodule 755, and an add/remove module 760. The operation of these modulesin certain exemplary embodiments will be described respectively withrespect to FIGS. 9-10, 11, 12-14, 15-16, and 17-18.

[0101] Start Up

[0102]FIG. 8 is an exemplary data flow diagram of a distributed searchbased technique's formation of service level A's service level topologyfor N1 of the optical network in FIG. 2 according certain embodiments ofthe invention. FIG. 9-11 are flow diagrams for a distributed searchbased technique for building service level topologies, using a set ofconnectivity constraints including QoS criteria and conversion freecriteria, in access nodes of an optical network. To provide an example,FIGS. 9-11 will be described with reference to the exemplary data flowdiagram of FIG. 8. The operations of this and other flow diagrams willbe described with reference to the exemplary embodiments of the otherdiagrams. However, it should be understood that the operations of theflow diagrams can be performed by embodiments of the invention otherthan those discussed with reference to these other diagrams, and theembodiments of the invention discussed with reference these otherdiagrams can perform operations different than those discussed withreference to the flow diagrams.

[0103]FIG. 9 is a flow diagram performed by each access node whenjoining an optical network according to embodiments of the invention.This flow diagram begins responsive to provision of wavelengthparameters and service level parameters (905). With reference to thedatabases in FIG. 7, this would occur responsive to the populating ofthe service level parameter database 710 and the link state database715. In certain embodiments, the service level parameter database ispopulated by the service provider through the network managementinterface.

[0104] In block 910, the number of service levels are determined andcontrol passes to block 915. In certain embodiments of the invention,block 910 is performed by parsing the service level parameter database.

[0105] As shown in block 915, for each link to an adjacent node, thelamdas on that link are classified by the service level parameters toform link service level channel sets. With reference to FIG. 8, the linkservice level channel set for service level A for each node shown inFIG. 8 is illustrated by a box next to that node. From block 915,control passes to block 920.

[0106] In block 920, a service level topology build-up is initiated foreach service level.

[0107]FIG. 10 is a flow diagram illustrating a service level topologybuild-up for a single service level according to embodiments of theinvention. Thus, the flow of FIG. 10 would be performed for each servicelevel responsive to block 920.

[0108] In block 1005, a service level topology structure is instantiatedand populated with any qualifying adjacent nodes (adjacent nodes forwhich this source node has any non-null link service channel sets atthis service level) and control passes to block 1010. With reference toFIG. 8, N1 would instantiate a service level topology structure 730 inits service level connectivity database 705. The service level topologystructure would include at its root N1, as well as a branch to each ofN2 and N3.

[0109] As shown, in block 1010, connectivity request message(s) aretransmitted to the qualifying adjacent node(s) and control passes toblock 1015. In certain embodiments of the invention, each connectivityrequest message includes a request ID, a source node ID, a forward nodeID, a service level, and a computed set (a set of one or more paths, aswell as the path service level channel set for each). While all of thesefields are not needed for block 1010 (e.g., the source node is the sameas the forward node, the needed information in the computed set isalready known by the adjacent nodes), they are used as the search movesthrough the network (see FIG. 11). While in certain embodiments of theinvention each connectivity request message includes the above notedfields, alternative embodiments could be implemented other ways (e.g.,while full versions of connectivity request message could be used forFIG. 11, reduced versions of connectivity request messages could be usedfor block 1010; such reduced versions could include simply the requestID, source node ID, and service level). With respect to FIG. 8, N1transmits a connectivity request message to each of N2 and N3 (thesource node ID is N1, and the service level is A).

[0110] In block 1015, the service level topology structure is updatedresponsive to connectivity response messages received. The nodestransmitting such connectivity response messages and the contents ofsuch connectivity response messages are described later herein withrespect to FIG. 11. For instance, upon receipt of a connectivityresponse message, the received data is added to the appropriate branchof the appropriate service level topology structure. Upon receipt of aconnectivity stop message, the path, identified in the received message,of the service level topology structure, for the service levelidentified in the received message, is complete. With respect to theexample optical network described herein, the service level topologystructure for service level A would represent something similar to thatshown in FIG. 3A. For example, in certain embodiments of the invention atable is maintained with each of the available paths and itscorresponding path service level channel set (e.g., each entry in thetable store one of the available paths and its corresponding pathservice level channel set).

[0111]FIG. 11 is a flow diagram illustrating operations performed bynodes responsive to a connectivity request message received over a linkaccording to certain embodiments of the invention. With respect of FIG.8, node N2 receives the connectivity request message from node N1.

[0112] In block 1110, it is determined if the connectivity requestmessage was previously processed. If so, control passes to block 1115;at which point this flow is complete. Otherwise, control passes to block1120. A connectivity request message could have been previouslyprocessed because it was received from a different adjacent node. Thedetermination as to whether a connectivity request message waspreviously processed could be performed in a number of different ways.For example, in an embodiment in which connectivity request messagesinclude the request ID and the source node ID, this determination can bemade by comparing this request ID and source node ID of the currentconnectivity request message to a log of such for previous connectivityrequest messages.

[0113] As shown in block 1125, the intersection of the received pathservice level channel set for the path to this node with the linkservice level channel set for each propagation port is determined. Fromblock 1125, control passes to block 1130. The phrase propagation port isused to refer to any ports other than: 1) the one the connectivityrequest message was received on; and 2) a port connected to the sourcenode (i.e., the source node is adjacent to this node). In certainembodiments of the invention, the propagation ports are determined byselecting links from the link state database that are not connected tothe forward node ID and source node ID identified in the connectivityrequest message. With reference to FIG. 8, since N2 received theconnectivity request over the link to N1 and since N1 is the sourcenode, N2 would select the port through which a link to node N4 isconnected. N2 would then determine the intersection of the path servicelevel channel set for N1:N2 with the link service level channel set forN2:N4. This intersection set is the path service level channel set forN1:N2:N4 and is included in the computed set (path service level channelsets are shown in FIG. 8 by dashed boxes, such as the one under N2).Specifically, N2 determines the intersection of the path service levelchannel set (SA (N1:N2)=lamda 1, 2) and the link service level channelset (SA (N2:N4)=lamda 1) to be lamda 1 (which is also represented hereinusing the format SA (N1:N2:N4)=lamda 1).

[0114] Thus, the computed set represents the intersection of thepreceding link service level channel sets for the path the connectivityrequest message has traveled. In the case of block 1010, the computedset is the same as the link service level channel set for the link overwhich the connectivity request message was transmitted. However, as theconnectivity request message gets retransmitted to other nodes, thecomputed set will represent the paths traveled and the intersection setfor each such path.

[0115] In block 1130, it is determined if there are any non-nullintersection sets. If so, control passes to block 1140. Otherwise,control passes to block 1135.

[0116] As shown in block 1140, a connectivity response message, with theintersection set(s) as path service level channel set(s), is transmittedto the source node and control passes to block 1145. In certainembodiments of the invention, each connectivity response messageincludes the service level, request ID, response node ID, and computedset. With regard to node N2, N2 would transmit to N1 a connectivityresponse message including as the computed set N1:N2:N4, lamda 1.

[0117] In block 1145, a connectivity request message, with theintersection set(s) as path service level channel set(s), is transmittedon the propagation ports and control passes to block 1115. With regardto node N2, N2 would transmit to N4 a connectivity request message. Withregard to embodiments of the invention in which connectivity requestmessages include request ID, a source node ID, a forward node ID, aservice level, and a computed set, N2 would respectively fill thesefields with the request ID, N1, N2, A, and the computed set N1:N2:N4,lamda 1.

[0118] In block 1135, a connectivity stop message is transmitted back tothe source node and control passes to block 1115. In certainembodiments, such a connectivity stop message includes the source nodeID.

[0119] To complete the example of FIG. 8, responsive to the connectivityrequest message from N1, N3 determines the intersection set to N4 forservice level A. N3 transmits this intersection set back to N1 in aconnectivity response message, as well as to N4 in a connectivityrequest message. Meanwhile, responsive to N2's connectivity requestmessage, N4 determines intersection sets to N3 and N5 for service levelA. N4 transmits these back to N1 in a connectivity response message andtransmits these to N3 and N5 in connectivity request messages.Responsive to N4's connectivity request messages: 1) N3 does nothingbecause it has seen this request ID before (the above connectivityrequest message from N1); and 2) N5 transmits back to N1 a connectivitystop message. Responsive to N3's connectivity request message, N4 doesnothing because it has seen this request ID before (the aboveconnectivity request message from N2).

[0120] Allocate

[0121]FIGS. 12-14 are flow diagrams illustrating the allocation of apath according to certain embodiments of the invention. FIG. 12 is theflow diagram illustrating operations performed by an access node toallocate a path according to certain embodiments of the invention. Theoperations in FIG. 12 result in: 1) update routing database message(s)being sent to the nodes along the selected path being allocated; and 2)update allocate channel message(s) being sent to certain nodes that areon that path. FIG. 13 is a flow diagram illustrating the operationsperformed by an access node responsive to an update routing databasemessage according to certain embodiments of the invention; FIG. 14 is aflow diagram illustrating the operations performed by an access noderesponsive to an update allocate channel message according to certainembodiments of the invention.

[0122] With reference to FIG. 12, an access node (which will act as thesource node) receives a demand for a path and control passes to block1210. There are various mechanisms through which such a demand for apath could be received by the access node. For instance, in certainembodiments of the invention OIF-UNI and/or OIF-NNI interfacingprotocols are used to communicate with nodes and domains, respectively,which do not support GMPLS or MPLS.

[0123] In block 1210, the service level and destination node for thedemand are determined and control passes to block 1220. Block 1210 maybe performed in a similar manner to block 605 of FIG. 6.

[0124] As shown in block 1220, it is determined if there is a pathavailable at that service level. If not, control passes to block 1225.Otherwise, control passes to block 1230. Block 1220 can be implementedin a variety of ways. With regard to the exemplary embodiment of FIG. 7,the service level topology structure is parsed to determine if thedestination node is reachable and there is an unallocated lamdaavailable. While in certain embodiments, the service level topologystructure is parsed responsive to a demand, alternative embodiments ofthe invention generate derivative structures that are faster to parseand/or pre-select (and may pre-allocate) various paths (e.g., seediscussion later herein). Block 1220 is similar to block 615 of FIG. 6.

[0125] As shown in block 1225, alternative action is taken. Block 1225is similar to block 625, and the various alternatives discussed thereare equally applicable here.

[0126] In block 1230, a path and channel are selected based uponselection criteria and control passes to block 1235. In certainembodiments, the selection of path and channel includes the selection ofa node: channel: port sequence for the path (it should be noted thatwhere, as here, a conversion-free connectivity constraint is used, asingle channel is used). Various embodiments can use different selectioncriteria for selecting the path and channel. For instance, certainembodiments of the invention utilize load balancing as described laterherein. It should also be understood that various path calculationtechniques may be used, including Djikstra's algorithm.

[0127] As shown in block 1235, the routing database is updated andcontrol passes to block 1240. The routing database is updated to reflectthe connection of the incoming port identified by the demand in block1205 with the outgoing channel: port of the selected path. In certainembodiments, responsive to the updating the routing database, well-knowntechniques are used to modify the data plane of the access nodeaccordingly (of course, alternative embodiments may be implemented tomodify the data plane first and/or through a different mechanism).Whether a path in the opposite direction is also allocated depends onwhether the implementation requires all paths to be bi-directionaland/or a bi-directional path was requested in the demand.

[0128] In block 1240, update routing database message(s) are transmittedto nodes on the selected path and control passes to block 1245. Incertain embodiments of the invention, each update routing databasemessage includes an update ID, as well as the channel and portinformation relevant to the recipient node of the message.

[0129] As shown in block 1245, the selected service level topologystructure is updated and control passes to block 1250. In particular,the selected channel is marked as allocated in all path service levelchannel sets down stream of a link in the selected path. In other words,the selected channel is marked allocated in the path service levelchannel set(s) of the available path(s) that include one or more linksof the selected path. To provide an example, assume the path N1: N2: N4is allocated with lamda 1 in FIG. 2. With reference to FIG. 3A, lamda 1would need to be marked as allocated from the path service level channelset of N1: N2, N1: N2: N4, N1: N2: N4: N3, N1: N2: N4: N5, and N1: N3:N4: N2 because each contains one or more links on the selected path.

[0130] In block 1250, an update allocate channel message is transmittedto nodes in the selected service level topology structure. In certainembodiments, each update allocate channel message includes an update ID,a service level, a path, an allocated channel, and a sent-to-set. Thesent-to-set represents the set of nodes to which the message is going tobe sent. While the nodes to which the message is to be sent can bedetermined in a variety of ways, certain embodiments of the inventionparse the service level topology structure to identify all of the nodes(removing duplicates) apart from the source node.

[0131]FIG. 13 is a flow diagram illustrating operations performed by anaccess node responsive to an update routing database message accordingto certain embodiments of the invention. In block 1310, the routingdatabase is updated. The receiving node's routing database is updated toreflect the connection identified in the received message. In certainembodiments, responsive to the updating of the routing database,well-known techniques are used to modify the data plane of the accessnode accordingly (of course, alternative embodiments may be implementedto modify the data plane first and/or through a differentmechanism—e.g., signaling).

[0132] Block 1310 is performed in a similar fashion to block 1235 ofFIG. 12.

[0133]FIG. 14 is a flow diagram illustrating operations performed by anaccess node responsive to an update allocate channel message accordingto certain embodiments of the invention. In block 1410, it is determinedif any of the available paths of the service level topology structurefor the service level of the allocated path contain one or more links ofthe selected path. If not, control passes to block 1415 where the flowdiagram ends. If so, control passes to block 1420. In certainembodiments of the invention, block 1410 is performed by parsing theappropriate service level topology structure to determine if any linkson the selected path are represented therein.

[0134] As shown in block 1420, it is determined if any of the pathservice level channel set(s) of the available paths identified in block1410 include the allocated wavelength. If not, control passes to block1415. Otherwise, control passes to block 1425. In certain embodiments ofthe invention, block 1420 is performed by parsing the path service levelchannel set(s) of the identified path(s) to determine if the allocatedwavelength is present.

[0135] As shown in block 1425, the selected service level topologystructure is updated and control passes to 1430. In certain embodimentsof the invention, block 1425 is performed by marking the allocatedwavelength as allocated in the path service level channel set(s)identified in block 1420.

[0136] As shown in block 1430, nodes are selected from the service leveltopology structure that are not identified in the received allocatechannel message and control passes to block 1435. In certain embodimentsof the invention, block 1430 is performed by: 1) identifying as “newset” all of the nodes in the service level topology structure that arenot in the sent-to-set in the received update allocate channel message(1405); and 2) forming an updated version of the sent-to-set that is theunion of the new set and the sent-to set in the received update allocatechannel message (1405).

[0137] In block 1435, an update allocated channel message is transmittedto the selected nodes. In certain embodiments of the invention, block1435 is performed by transmitting an update allocate channel messagewith the updated sent-to-set to all nodes in the new set of block 1430.

[0138] Deallocate

[0139] Responsive to a request to deallocate a channel (e.g.,communication received by the source node for the path using thechannel), signaling is used to disconnect the existing cross connects onthe path. FIG. 15 is a flow diagram illustrating operations performed bythe source node of a path responsive to that path being deallocatedaccording to certain embodiments of the invention. As part of the flowdiagram in FIG. 15, the source node of the path transmits updatedeallocate channel message(s) to certain other nodes. FIG. 16 is a flowdiagram illustrating the operations performed by access nodes responsiveto receiving an update deallocate channel message according to certainembodiments of the invention.

[0140] In block 1510, the service level of the channel being deallocatedis determined and control passes to block 1515. In certain embodiments,the service level is determined by parsing the link state database tolocate the channel being deallocated.

[0141] As shown in block 1520, the service level topology structure isupdated and control passes to block 1525. Block 1520 is performed in asimilar fashion to block 1245, with the exception that the channel ismarked unallocated. In particular, the deallocated channel is marked asunallocated in all path service level channel sets down stream of a linkin the deallocated path. In other words, the deallocated channel ismarked unallocated in the path service level channel set(s) of theavailable path(s) that include one or more links of the deallocatedpath. To provide an example, assume the path N1: N2: N4 is deallocatedwith lamda 1 in FIG. 2. With reference to FIG. 3A, lamda 1 would need tobe marked as unallocated from the path service level channel set of N1:N2, N1: N2: N4, N1: N2: N4: N3, N1: N2: N4: N5, and N1: N3: N4: N2because each contains one or more links on the deallocated path.

[0142] As shown in block 1525, an update deallocate channel message istransmitted to nodes in the service level topology structure and controlpasses to block 1530. The set of nodes to which this message is sent isreferred to the sent-to-set. In certain embodiments of the invention,the update deallocate channel message includes the source node ID, theadjacent node ID, the path, the channel deallocated, the update ID, theservice level, and the sent-to-set. While the nodes to which the messageis to be sent can be determined in a variety of ways, certainembodiments of the invention parse the service level topology structureto identify all of the nodes (removing duplicates) apart from the sourcenode.

[0143] As shown in block 1530, the routing database is updated andcontrol passes to block 1540. With reference to the exemplary embodimentof FIG. 7, the routing database 720 would be modified to remove theconnection of the deallocated channel. Whether a path in the oppositedirection is also deallocated depends on whether the implementationrequires all paths to be bi-directional and/or the path beingdeallocated was bi-directional.

[0144] In block 1540, update routing database message(s) are transmittedto nodes on the selected path. In certain embodiments of the invention,each update routing database message includes an update ID, as well asthe channel and port information relevant to the recipient node of themessage. A recipient access node responds to the receipt of such amessage by modifying its routing database to reflect the disconnectionof the incoming channel:port and the outgoing channel: port as specifiedin the message.

[0145] In this manner, the nodes along the path are updated to reflectthe deallocation; in addition, update deallocate channel messages havebeen sent to initiate any necessary updating at such nodes.

[0146]FIG. 16 is a flow diagram illustrating operations performed byaccess nodes responsive to an update deallocate channel messageaccording to certain embodiments of the invention. In block 1610, it isdetermined if any of the available paths of the service level topologystructure for the service level of the deallocated path contain one ormore links of the deallocated path. If not, control passes to block 1615where the flow diagram ends. If so, control passes to block 1620. Incertain embodiments of the invention, block 1610 is performed by parsingthe appropriate service level topology structure to determine if anylinks on the deallocated path are represented therein.

[0147] As shown in block 1620, it is determined if any of the pathservice level channel set(s) of the available paths identified in block1610 include the deallocated wavelength. If not, control passes to block1615. Otherwise, control passes to block 1625. In certain embodiments ofthe invention, block 1620 is performed by parsing the path service levelchannel set(s) of the identified path(s) to determine if the allocatedwavelength is present.

[0148] As shown in block 1625, the selected service level topologystructure is updated and control passes to 1630. In certain embodimentsof the invention, block 1625 is performed by marking the deallocatedwavelength as unallocated in the path service level channel set(s)identified in block 1620.

[0149] In block 1630, the nodes in the service level topology structurethat are not identified in the received update deallocate channelmessage are selected and control passes to block 1635. In certainembodiments of the invention, block 1630 is performed by: 1) identifyingas “new set” all nodes in the service level topology structure that arenot in the sent-to-set in the received update deallocate channel message(1605); and 2) forming an updated version of the sent-to-set that is theunion of the new set and the sent-to-set in the received updatedeallocate channel message (1605).

[0150] As shown in block 1635, an update deallocate channel message issent to the selected nodes and control passes to block 1615. In certainembodiments of the invention, this update deallocate channel messageincludes the new sent-to-set determined in block 1630 as opposed to thesent-to-set in the received update deallocate channel message (1605).

[0151] Dynamic Provisioning

[0152] As previously noted, a request to change the demand criteria fora given provisioned service (e.g., a request to lower or raise theservice level of a given provisioned service) is also addressed bycertain embodiments of the invention. In particular, certain suchembodiments respond to such requests by allocating a new path, and ifsuccessful and necessary, moving the traffic from the old path to thenew allocated path and de-allocating the old path.

[0153] The reduced network topology database size (as compared to aphysical network topology database) and distributed nature of thissource based scheme allows for the provisioning of optical circuits inreal-time (or on the fly; that is, the demands do not need to know aheadof time). Furthermore, the QoS based criteria allows for differentiationof traffic types at the optical layer. Thus, for example, a givenservice to a customer can be at a higher service level during the day,and dropped down to the lower service level at night. Of course, suchswitches can occur even more often.

[0154] In addition, implementations can push SONET out to the edge ofthe network. For instance, as opposed to carrying stacks of networklayers (EP over ATM over SONET) over optical, network layers can bedirectly carried over optical (e.g., IP or ATM, or SONET).

[0155] Add and Remove Channels

[0156]FIGS. 17 and 18 are flow diagrams illustrating operationsperformed when either a channel is added or a channel without livetraffic is removed according to certain embodiments of the invention.The operations of FIG. 17 are performed by the access nodes connected bythe link on which the channel is added or removed (also referred to asthe adjoining nodes or the access nodes made adjacent by that link). Aspart of these operations, an update add/remove channel message istransmitted to certain other nodes. The operations of FIG. 18 areperformed by an access node responsive to such an update add/removechannel message.

[0157]FIG. 17 is a flow diagram illustrating the operations performed bythe access nodes connected by the link on which the channel isadded/removed according to certain embodiments of the invention. Inblock 1710, the service level of the channel is determined and controlpasses to block 1715. When a channel is being added, block 1710 isperformed, according to certain embodiments of the invention, bycomparing that channel's wavelength parameters to the service levelparameters to classify it into one of the service levels. When a channelis being removed, block 1710 is performed, according to certainembodiments of the invention, by accessing the link state database ofFIG. 7.

[0158] As shown in block 1715, a connectivity request message istransmitted on the link carrying the channel and control passes toblocks 1720 and 1725. Block 1715 is performed in a similar manner toblock 1515 of FIG. 15.

[0159] In block 1720, the service level topology structure is updatedresponsive to connectivity response messages received. In certainembodiments of the invention, block 1720 is performed in a similarmanner to block 1015 of FIG. 10 with a variation. Since certain dataalready exists in the service level topology structure, the receiveddata in the connectivity response messages is used to update (add,remove, and/or alter) the existing service level topology structure. Inthe case of a channel removal, in certain embodiments of the invention,the channel on each path with the link may be either removed from theservice level topology structure or marked broken.

[0160] As shown in block 1725, an update add/remove channel message istransmitted to the nodes in the service level topology structure thatare not on the link with the channel. In certain embodiments of theinvention, each update add/remove channel message includes an update ID,the wavelength, whether this is an addition or removal, the source nodeID, the source adjacent node ID, the service level, and the sent-to-set.The source node and the source adjacent node identified are the accessnodes connected by the link on which the channel was added/removed. Thesent-to-set includes the nodes in the service level topology structurethat the message is sent to in block 1725 (all nodes in the servicelevel topology structure other than the source node and source adjacentnode).

[0161]FIG. 18 is a flow diagram illustrating the operations performed byan access node responsive to receiving an update add/remove channelmessage according to certain embodiments of the invention. As shown inblock 1810, it is determined if the service level topology structureincludes path(s) with the link to which the channel was added/removed.If not, control passes to block 1815 where the flow diagram ends. If so,control passes to block 1820. In certain embodiments of the invention,block 1810 is performed by searching the service level topologystructure (for the service level identified in the received updateadd/remove channel message) for the link identified in the receivedupdate add/remove channel message (based on the source node ID andsource adjacent node ID contained therein).

[0162] In block 1820, connectivity request message(s) are transmitted onlink(s) of these paths and control passes to blocks 1825 and 1830. Inparticular, the access node transmits a connectivity request message oneach of its links that are part of these paths.

[0163] In block 1825, the service level topology structure is updatedresponsive to connectivity response messages received. Block 1825 isperformed in a similar fashion to block 1720 of FIG. 17.

[0164] As shown in block 1830, nodes are selected from the service leveltopology structure that are not identified in the received updateadd/remove channel message and control passes to block 1835. In certainembodiments of the invention, block 1830 is performed by: 1) identifyingas “new set” all of the nodes in the service level topology structurethat are not in the sent-to-set in the received update add/removechannel message (1805); and 2) forming an updated version of thesent-to-set that is the union of the new set and the sent-to set in thereceived update add/remove channel message (1805).

[0165] In block 1835, an update add/remove channel message istransmitted to the selected nodes. As before, this update add/removechannel message will: 1) identify whether this is an addition orremoval; and 2) include the updated sent-to-set as opposed to thesent-to-set in the received update add/remove channel message (1805).

[0166] With regard to the removal of a channel with live traffic, theflow in FIGS. 17 and 18 is followed with some variation. In particular,each involved access node (the access nodes connected by the link withthe channel and the access nodes that receive an update add/removechannel message), determines if they are the source node of anyallocated path(s) that includes the link and uses the removed channel.If so, that access node executes a redundancy (protection) scheme.

[0167] Link Removal

[0168] When a link is removed (e.g., it fails or is permanently removed)between two nodes within the network, all the channels on that link arelost. While certain embodiments perform the channel removal operationsof FIGS. 17 and 18 for each such channel, other embodiments of theinvention reduce the number of messages generated by addressing the linkas a whole. In particular, FIGS. 19 and 20 are flow diagramsillustrating operations performed when a link is removed according tocertain embodiments of the invention. The operations of FIG. 19 areperformed by the access nodes connected by the link (also referred to asthe adjoining nodes or the access nodes made adjacent by that link). Aspart of these operations, a link removal message is transmitted tocertain other nodes. The operations of FIG. 20 are performed by anaccess node responsive to such a link removal message.

[0169]FIG. 19 is a flow diagram illustrating the operations performed bythe access nodes connected by the removed link according to certainembodiments of the invention. Block 1910 is used to indicate that thefollowing blocks are performed for each service level.

[0170] As shown in block 1915, it is determined if the service leveltopology structure includes path(s) with the removed link. If not,control passes to block 1930. If so, control passes to block 1925. Incertain embodiments of the invention, block 1915 is performed bysearching the service level topology structure for the presence of theremoved link.

[0171] In block 1925, the service level topology structure is updatedand control passes block 1930. In certain embodiments of the invention,any of the channels in these path's path service level channel set(s)that are in common with the link service level channel set of theremoved link are marked broken (indicating that the channel(s) cannot beused). While in certain embodiments of the invention channels markedbroken are maintained indefinitely, other embodiments of the inventiondelete such marked channels (and corresponding paths) after a period oftime if the link is not reestablished. In other embodiments of theinvention, these path(s) and channels are simply deleted immediately andadded back in (see the link addition section) if they are reestablished.

[0172] As shown in block 1930, a link removal message is transmitted tothe nodes in the service level topology structure that are not on thelink. In certain embodiments of the invention, each link removal messageincludes the link service level channel set of the removed link, thesource node ID, the source adjacent node ID, an update ID, the servicelevel, and the sent-to-set. The source node and the source adjacent nodeidentified are the access nodes connect to the removed link. Thesent-to-set includes the nodes in the service level topology structurethat the message is sent to (all nodes in the service level topologystructure other than the source node and source adjacent node).

[0173]FIG. 20 is a flow diagram illustrating the operations performed byan access node responsive to receiving a link removal message accordingto certain embodiments of the invention. As shown in block 2010, it isdetermined if the service level topology structure includes path(s) withthe removed link. If not, control passes to block 2020. If so, controlpasses to block 2015. In certain embodiments of the invention, block2010 is performed by searching the service level topology structure (forthe service level identified in the received link removal message) forthe link identified in the received link removal message (based on thesource node ID and source adjacent node ID contained therein).

[0174] In block 2015, the service level topology structure is updatedand control passes block 2020. In certain embodiments of the invention,any of the channels in these path's (identified in block 2010) pathservice level channel set(s) that are in common with the link servicelevel channel set of the removed link are marked broken (indicating thatthe channel(s) cannot be used). While in certain embodiments of theinvention channels marked broken are maintained indefinitely, otherembodiments of the invention delete such marked channels (andcorresponding paths) after a period of time if the link is notreestablished. In other embodiments of the invention, these path(s) andchannels are simply deleted immediately and added back in (see the linkaddition section) if they are reestablished.

[0175] As shown in block 2020, nodes are selected from the service leveltopology structure that are not identified in the received link removalmessage and control passes to block 2025. In certain embodiments of theinvention, block 2020 is performed by: 1) identifying as “new set” allof the nodes in the service level topology structure that are not in thesent-to-set in the received link removal message (2005); and 2) formingan updated version of the sent-to-set that is the union of the new setand the sent-to set in the link removal message (2005).

[0176] In block 2025, an link removal message is transmitted to theselected nodes. As before, this link removal message will include theupdated sent-to-set as opposed to the sent-to-set in the received linkremoval message (2005).

[0177] With regard to the removal of a link with live traffic, the flowin FIGS. 19 and 20 is followed with some variation. In particular, eachinvolved access node (the access nodes connected by the removed link andthe access nodes that receive the link removal message), determines ifthey are the source node of any allocated path(s) that includes thelink. If so, that access node executes a redundancy (protection) scheme.

[0178] Link Addition

[0179] When a link is added, the LSD is updated in the access nodesconnected to the link (e.g., in certain embodiments of the invention,LMP recognizes the new link). When a link is added between two nodeswithin the network, a number of channels on that link can be availableall at once. While certain embodiments perform the channel additionoperations of FIGS. 17 and 18 for each such channel, other embodiment ofthe invention reduce the number of messages generated by addressing thelink as a whole. In particular, FIGS. 21 and 22 are flow diagramsillustrating operations performed when a link is added according tocertain embodiments of the invention. The operations of FIG. 21 areperformed by the access nodes connected by the link (also referred to asthe adjoining nodes or the access nodes made adjacent by that link). Aspart of these operations, a link addition message is transmitted tocertain other nodes. The operations of FIG. 22 are performed by anaccess node responsive to such a link addition message.

[0180]FIG. 21 is a flow diagram illustrating the operations performed bythe access nodes connected by the added link according to certainembodiments of the invention. In block 2107, the wavelength(s) on theadded link are classified by service level parameters to form linkservice level channel set(s) and control passes to block 2110. Incertain embodiments of the invention, block 2107 is performed in asimilar manner to block 915, with the exception that only the added linkis processed.

[0181] Block 2110 is used to indicate that the following blocks areperformed for each service level to which new channels were added (thoseservice levels for which the link service level channel set of the addedlink is not null).

[0182] As shown, in block 2115, connectivity request message(s) aretransmitted to the qualifying adjacent node(s) and control passes toblocks 2120 and 2125. In certain embodiments, block 2115 is performed ina similar manner to block 1010.

[0183] In block 2120, the service level topology structure is updated.In certain embodiments of the invention, block 2120 is performed in asimilar manner to blocks 1005 and 1015 of FIG. 10 with a variation. Withregard to the variation on block 1005, the service level topologystructure is populated with the access node made adjacent by the addedlink (the service level topology structure was already populated withany other adjacent nodes). With regard to the variation on block 1015,since certain data already exists in the service level topologystructure, the received data in the connectivity response messages isused to update the existing service level topology structure (add whatis not already present).

[0184] In block 2125, a link addition message is transmitted to nodes inthe selected service level topology structure. In certain embodiments,each link addition message includes a service level and a sent-to-set(all of the nodes in the service level topology apart from the sourcenode).

[0185]FIG. 22 is a flow diagram illustrating the operations performed byan access node responsive to receiving a link addition message accordingto certain embodiments of the invention.

[0186] As shown, in block 2210, connectivity request message(s) aretransmitted to the qualifying adjacent node(s) and control passes toblocks 2215 and 2220. In certain embodiments, block 2210 is performed ina similar manner to block 1010.

[0187] In block 2215, the service level topology structure is updatedresponsive to connectivity response messages received. Block 2215 isperformed in a similar fashion to block 1015 of FIG. 10 with avariation. With regard to the variation on block 1015, since certaindata already exists in the service level topology structure, thereceived data in the connectivity response messages is used to updatethe existing service level topology structure (add what is not alreadypresent).

[0188] As shown in block 2220, nodes are selected from the service leveltopology structure that are not identified in the received link additionmessage and control passes to block 2225. In certain embodiments of theinvention, block 2220 is performed by: 1) identifying as “new set” allof the nodes in the service level topology structure that are not in thesent-to-set in the received link addition message (2205); and 2) formingan updated version of the sent-to-set that is the union of the new setand the sent-to set in the link addition message (2205).

[0189] In block 2225, a link addition message is transmitted to theselected nodes. As before, this link addition message will include theupdated sent-to-set as opposed to the sent-to-set in the received linkaddition message (2005).

[0190] Node Removal

[0191] When a node is removed, the LSD is updated in the adjacent accessnode(s) (e.g., in certain embodiments of the invention, LMP recognizesthe removal of the node). When a node is removed, the channels on itslink(s) are no longer available all at once. While certain embodimentsperform the link removal operations of FIGS. 19 and 20 for each suchlink, other embodiment of the invention reduce the number of messagesgenerated by addressing the node as a whole. In particular, FIGS. 23 and24 are flow diagrams illustrating operations performed when a node isremoved according to certain embodiments of the invention. Theoperations of FIG. 23 are performed by the adjacent access node(s). Aspart of these operations, a node removal message is transmitted tocertain other nodes. The operations of FIG. 24 are performed by anaccess node responsive to such a node removal message.

[0192]FIG. 23 is a flow diagram illustrating the operations performed bythe access node(s) adjacent a removed node according to certainembodiments of the invention. Block 2310 is used to indicate that thefollowing blocks are performed for each service level.

[0193] In block 2315, the service level topology structure is updatedand control passes to block 2320. In certain embodiments of theinvention, block 2315 is performed by removing from the service leveltopology structure the branch, if one exists, that has as the first hopthe removed node.

[0194] As shown in block 2320, it is determined if the service leveltopology structure includes path(s) with the removed node. If not,control passes to block 2325 where the flow diagram ends. If so, controlpasses to block 2330. In certain embodiments of the invention, block2320 is performed by searching the service level topology structure forthe presence of the removed node.

[0195] As shown, in block 2330, connectivity request message(s) aretransmitted on link(s) of these paths and control passes to blocks 2335and 2340. In particular, the access node transmits a connectivityrequest message on each of its links that are part of these paths.

[0196] In block 2335, a new service level topology structure isinstantiated and updated responsive to connectivity response messagesreceived. In certain embodiments, block 2325 is performed in a similarmanner as blocks 1005 and 1015 with a variation. In particular, the newservice level topology structure preserves the channel states from thecurrent service level topology structure (which is kept until the newservice level topology structure is completed).

[0197] In block 2340, a node removal message is transmitted to nodes inthe selected service level topology structure. In certain embodiments ofthe invention which instantiate a new service level topology structureas in block 2325, the service level topology structure used for block2330 is the current service level topology structure. In certainembodiments, each link removal message includes a removed node ID, aservice level, and a sent-to-set (all of the nodes in the service leveltopology apart from the removed node and the nodes adjacent the removednode).

[0198]FIG. 24 is a flow diagram illustrating the operations performed byan access node responsive to receiving a node removal message accordingto certain embodiments of the invention.

[0199] In block 2410, it is determined if the service level topologystructure includes path(s) with the removed node. If not, control passesto block 2415 where the flow diagram ends. If so, control passes toblock 2420. In certain embodiments of the invention, block 2410 isperformed by searching the service level topology structure for thepresence of the removed node.

[0200] As shown, in block 2420, connectivity request message(s) aretransmitted on link(s) of these paths and control passes to blocks 2425and 2430. In particular, the access node transmits a connectivityrequest message on each of its links that are part of these paths.

[0201] In block 2425, a new service level topology structure isinstantiated and updated responsive to connectivity response messagesreceived. In certain embodiments, block 2425 is performed in a similarmanner as blocks 1005 and 1015 with a variation. In particular, the newservice level topology structure preserves the channel states from thecurrent service level topology structure (which is kept until the newservice level topology structure is completed).

[0202] As shown in block 2430, nodes are selected from the service leveltopology structure that are not identified in the received node removalmessage and control passes to block 2435. In certain embodiments of theinvention, block 2430 is performed by: 1) identifying as “new set” allof the nodes in the current service level topology structure that arenot in the sent-to-set in the received node removal message (2405); and2) forming an updated version of the sent-to-set that is the union ofthe new set and the sent-to set in the node removal message (2405).

[0203] In block 2435, a node removal message is transmitted to theselected nodes. As before, this node removal message will include theupdated sent-to-set as opposed to the sent-to-set in the received noderemoval message (2005).

[0204] While in certain embodiments of the invention, nodes and theirpaths are deleted immediately and added back in (see the node additionsection) if they are reestablished, alternative embodiments provideother mechanisms (e.g., in certain embodiments of the invention thepaths are marked broken are maintained indefinitely, in otherembodiments of the invention the paths are marked broken and deletedafter a period of time if the node is not reestablished, etc.).

[0205] Node Addition

[0206] When a node is added, the added node performs the flows in FIGS.9 and 10. In addition, the LSD is updated in the adjacent access node(s)(e.g., in certain embodiments of the invention, LMP recognizes theremoval of the node). Additionally, for each of the adjacent nodes,there has effectively been one or more links added to the new node. Assuch, each of the adjacent node(s) performs the flow of FIG. 21, withthe exception that block 2125 is replaced with a different operation. Inparticular, instead of block 2125, a node addition message istransmitted to nodes in the selected service level topology structure.In certain embodiments, each node addition message includes an addednode ID, a service level and a sent-to-set. The message is sent to, andthe sent-to-set includes, any nodes in the service level topology apartfrom the source node.

[0207]FIG. 25 is a flow diagram illustrating the operations performed byan access node responsive to receiving a node addition message accordingto certain embodiments of the invention.

[0208] As shown, in block 2510, connectivity request message(s) aretransmitted to the qualifying adjacent node(s) and control passes toblocks 2515 and 2520. In certain embodiments, block 2510 is performed ina similar manner to block 1010.

[0209] In block 2515, a new service level topology structure isinstantiated and updated responsive to connectivity response messagesreceived. In certain embodiments, block 2515 is performed in a similarmanner as blocks 1005 and 1015 with a variation. In particular, the newservice level topology structure preserves the channel states from thecurrent service level topology structure (which is kept until the newservice level topology structure is completed).

[0210] As shown in block 2520, nodes are selected from the service leveltopology structure that are not identified in the received node additionmessage and control passes to block 2525. In certain embodiments of theinvention, block 2520 is performed by: 1) identifying as “new set” allof the nodes in the current service level topology structure that arenot in the sent-to-set in the received node addition message (2505); and2) forming an updated version of the sent-to-set that is the union ofthe new set and the sent-to set in the node addition message (2505).

[0211] In block 2525, a node addition message is transmitted to theselected nodes. As before, this node addition message will include theupdated sent-to-set as opposed to the sent-to-set in the received nodeaddition message (2505).

[0212] Service Level Parameter Changes

[0213] In certain embodiments of the invention, the service provider mayupdate the service level parameters and push a fresh copy on each node.If and when a new QoS criteria is added, certain embodiments of theinvention perform the following:

[0214] 1. The contents of the service level parameters database iscopied and kept in the memory.

[0215] 2. The service level parameters database is populated with newdata.

[0216] 3. Blocks 915 and 920 are performed to create new service leveltopology structures, keeping the existing service level topologystructure for each service level.

[0217] 4. The new service level topology structures are used for newconnections.

[0218] 5. The previous service levels are mapped to the current servicelevels by comparing the parameters.

[0219] 6. The connection status from the old service level topologiesare mapped to the new service level topology structures to relevantservice levels.

[0220] 7. The old service level topologies are deleted.

[0221] Similarly, if an when an existing service level parameter(s) ischanged, certain embodiments of the invention perform the following:

[0222] 1. The contents of the particular level in service levelparameters database is copied and kept in the memory.

[0223] 2. The service level parameters database is populated with newdata.

[0224] 3. New service level topology structures are built for theupdated levels keeping the old service level topology structures.

[0225] 4. The new service level topology structures are used for newconnections.

[0226] 5. The previous service levels are mapped to the current servicelevels by comparing the parameters.

[0227] 6. The connection status from the old service level topologiesare mapped to the new service level topology structures to relevantservice levels.

[0228] 7. The old service level topologies are deleted.

[0229] Of course, alternative embodiments may handle such changes inother ways.

[0230] Exemplary Load Balancing

[0231] Where there are multiple shortest paths available, the issue ofload balancing comes into play. For instance, certain embodiments of theinvention implement load balancing to allow the service provider someoptions. Specifically, when a demand is received, there can eitherbe: 1) a set of multiple shortest paths; or 2) a single shortest path.Where there is a set of multiple shortest paths, wavelengths areselected from each member of the set in round robin fashion. However,when there is a single shortest path, either one of two schemes is used.In the first scheme, a threshold is specified (e.g., specified by theservice provider) for any link in the network. If the number of channelsfor a particular service level crosses the threshold on that link, thenthat link becomes unavailable for any future demand. This allows theservice provider to tailor the traffic flow on the network. In thesecond scheme, a distribution ratio system is used. Specifically, theratio is the number of new paths “allocated to non-shortest path” to“the shortest path.”

[0232] Exemplary Contention Resolution

[0233] Since requests for paths by different access nodes may overlap,there is a need for contention resolution. Certain embodiments of theinvention resolve contention issues by giving priority to the sourcewith the higher IP number. However, this brings in a special case wherea source node may be receiving demand request at a higher frequency thanthe other source node. The other source node, thus, potentially maystarve.

[0234] Other embodiments of the invention use one of the followingcontention resolution schemes to overcome this deficiency.

[0235] 1. One such scheme is to pre-allocate a lightpath for the nextdemand in advance. This result in each access node preallocatinglightpaths to each accessible node at each service level. As such, thisscheme can put a relatively high amount of strain on network resources.

[0236] 2. Another such scheme is referred to herein as highest servicelevel preallocation. Instead of preallocating lightpaths to eachaccessible node for each service level, this is done only for thehighest service level. In the case of an unfavorable settlement ofcontention during demand allocation, the demand is allocated on thepreallocated lightpath at the highest service level. As such, thisscheme puts a relatively lower amount of strain on network resources,but can cause the highest service level lightpaths to get used up thefastest.

[0237] 3. Yet another such scheme is referred to herein as defaultservice level preallocation. In particular, for each source todestination pair, an indication of the default service level ismaintained (e.g., the most common service level for historicallyreceived demands). Instead of preallocating lightpaths to eachaccessible node for each service level or preallocating lightpaths toeach accessible node at the highest service level, preallocation is doneonly for the default service level for each source to destination pair.In the case of an unfavorable settlement of contention during demandallocation, the demand is allocated on the preallocated lightpath at thedefault service level. As such, this scheme puts a relatively loweramount of strain on network resources than scheme 1 and attempts toavoid using up the highest service level the fastest by predicting themost common service level.

[0238] Aggregating

[0239] While embodiments have been described in which separate messagesare transmitted, alternative embodiments aggregate different ones ofsuch messages. For instance, certain embodiments aggregate messages fordifferent service level topologies during startup.

ALTERNATIVE EMBODIMENTS

[0240] While various embodiments of the invention has been described,alternative embodiments of the invention can operate differently. Forinstance, while the flow diagrams in the figures show a particular orderof operations performed by certain embodiments of the invention, itshould be understood that such order is exemplary (e.g., alternativeembodiments may perform the operations in a different order, combinecertain operations, overlap certain operations, etc.) In addition, whilecertain embodiments have been described that operate to reduce thenumber of communications between nodes by transmitting messages to onlyselected nodes (e.g., blocks 1250, 1320, 1430/1435, 1525, 1630/1635,1725, and 1830/1835), alternative embodiments may be implemented totransmit such messages to more, less, or different nodes using differentschemes (e.g., certain alternative embodiments broadcast each suchmessage to every node). As another example, while certain embodiments ofthe invention have been described with respect to distributed searchtechniques for building/maintaining network topology databases and withrespect to a source based scheme, alternative embodiments could beimplemented different ways or combinations of ways (e.g., centralizednetwork topology database building/maintaining, centralizedprovisioning, hybrids, etc.).

[0241] While the invention has been described in terms of severalembodiments, those skilled in the art will recognize that the inventionis not limited to the embodiments described, can be practiced withmodification and alteration within the spirit and scope of the appendedclaims. The description is thus to be regarded as illustrative insteadof limiting.

What is claimed is:
 1. A method comprising: applying a set of one ormore connectivity constraints that include quality of service (QoS)based criteria on a physical network topology of a wave length divisionmultiplexing optical network to divide said optical network intoseparate service levels; and determining service level topologies foreach of said service levels.
 2. The method of claim 1, wherein said QoSbased criteria includes one or more of bandwidth, bit error rate,optical signal to noise ration, peak noise level, and re-routingpriority.
 3. The method of claim 1, wherein said determining includesdetermining, for each service level, a service level topology for thenetwork.
 4. The method of claim 1, wherein said determining includesdetermining, for each service level, a service level topology for eachnode of the optical network.
 5. The method of claim 1, wherein said setof connectivity constraints also includes a set of one or moreconversion criteria.
 6. The method of claim 1, wherein said set ofconnectivity constraints also includes a conversion free connectivityconstraint.
 7. A method comprising: maintaining a classification by QoScriteria of wavelengths for each link of a wave length divisionmultiplexing optical network, said QoS criteria defining a plurality ofservice levels; and for each of said plurality of service levels,maintaining service level connectivity based on a conversion criteria.8. The method of claim 7, wherein said QoS based criteria includes oneor more of bandwidth, bit error rate, optical signal to noise ration,peak noise level, and re-routing priority.
 9. The method of claim 7,further comprising: tracking said wavelengths for each of said links byoperating a link management protocol in each of the nodes of the opticalnetwork.
 10. The method of claim 7, wherein said maintaining saidclassification includes comparing parameters of each of the wavelengthsto service level parameters, wherein there is a service level parameterfor each of said plurality of service levels for each of said QoScriteria.
 11. The method of claim 10, wherein said maintaining saidclassification includes each node of said optical network performingsaid comparing.
 12. The method of claim 7, wherein the service levelconnectivity for each of said plurality of service levels includes theavailable wavelengths and the status as either allocated or unallocated.13. The method of claim 7, wherein said conversion criteria representsthe number of wavelength conversion s allowable for a given opticalcircuit.
 14. An apparatus comprising: a wavelength division multiplexingoptical network supporting a plurality of service levels, whereindifferent wavelengths on at least certain links of said optical networkqualify for different ones of said plurality of service levels; and atleast one separate network topology database for each of said pluralityof service levels that represents the connectivity between nodes of saidoptical network using those of the wavelengths that qualify for thatservice level.
 15. The apparatus of claim 14, wherein the connectivityis conversion free connectivity.
 16. The apparatus of claim 14, whereinsaid network topology databases are stored in a centralized networkserver.
 17. The apparatus of claim 14, wherein each access node of saidoptical network stores a separate one of said network topology databasesfor each of said plurality of service levels.
 18. An apparatuscomprising: for each wavelength on each link of a wavelength divisionmultiplexing optical network, a wavelength parameter for each of a setof QoS based criteria; for each of a plurality of service levels, aservice level parameter for each of said set of QoS based criteria; foreach link of said optical network, a link service level channel set foreach of said plurality of service levels representing those of thewavelengths on that link with parameters meeting the service levelparameters of that service level; and for each access node of saidoptical network, a service level topology structure for each of saidplurality of service levels representing connectivity of that accessnode to others of said access nodes using wavelengths from the linkservice level channel sets of that service level.
 19. The apparatus ofclaim 18, wherein said QoS based criteria includes one or more ofbandwidth, bit error rate, optical signal to noise ration, peak noiselevel, and re-routing priority.
 20. The apparatus of claim 18, whereineach access node of said optical network stores the link service levelchannel sets of those of the links connected to that access node. 21.The apparatus of claim 18, wherein said service level topologystructures are stored in a centralized network server.
 22. The apparatusof claim 18, wherein each access node stores those of said service leveltopology structures representing connectivity of that access node. 23.The apparatus of claim 18, wherein each of said service level topologystructures stores those paths for which the intersection of the linkservice level channel sets of the links of that path is not null.
 24. Anapparatus comprising: an access node, to be coupled in a wavelengthdivision multiplexing optical network, including, a link state databaseto store, for each link connected to said access node, a link statestructure to store a port of the access node to which that link isconnected, available wavelengths on that link, and parameters of thosewavelengths; a service level parameter database to store, for each of aset of one or more supported service levels, a service level parameterfor each of a set of QoS based criteria; and a service levelconnectivity database to store, for each of said set of service levels,a service level topology structure that stores a representation of theservice level topology of that service level for said access node. 25.The apparatus of claim 24, wherein said QoS based criteria includes oneor more of bandwidth, bit error rate, optical signal to noise ration,peak noise level, and re-routing priority.
 26. The apparatus of claim24, wherein each of said service level topology structures stores pathsto those of other access nodes of said optical network that can bereached with those of said wavelengths that qualify for the servicelevel of that service level topology structure.
 27. The apparatus ofclaim 24, wherein each of said service level topology structures storesavailable paths to other access nodes in said optical network.
 28. Theapparatus of claim 27, wherein each of said paths is a series of two ormore nodes connected by links on which there are wavelengths at theservice level of that path.
 29. The apparatus of claim 27, wherein eachof said paths is a set of one or more links and a set of wavelengthsthat are at the service level of that path and that are available onevery one of said set of links.
 30. The apparatus of claim 24, whereinsaid access nodes also includes a set of one or more modules to,responsive to request to change the service level of a given provisionedservice, allocate a new communication path at a different one of theservice levels than a previous communication path, begin routing trafficof the service on the new communication path, and deallocate theprevious communication path.
 31. A method for an access node of awavelength division multiplexing optical network, said methodcomprising: for each link to an adjacent node of said wavelengthdivision multiplexing optical network, said access node classifyingwavelengths on that link according to a set of one or more service levelparameters for each of a plurality of service levels; for each of saidplurality of service levels, instantiate a service level topologystructure; and responsive to receiving information regardingconnectivity at each of said plurality of service levels to other accessnodes in said optical network, adding such information to said servicelevel topology structure for that service level.
 32. The method of claim31, wherein said classifying is based on one or more of bandwidth, biterror rate, optical signal to noise ration, peak noise level, andre-routing priority.
 33. The method of claim 31, further comprising: foreach link to an adjacent node, tracking said wavelengths by operating alink management protocol.
 34. The method of claim 31, wherein saidclassifying includes comparing parameters of each of the wavelengths tothe sets of service level parameters.
 35. The method of claim 31,wherein said adding includes, for each of said service level topologystructures, storing paths to those of other access nodes of said opticalnetwork that can be reached with those of said wavelengths that qualifyfor the service level of that service level topology structure.
 36. Themethod of claim 35, wherein each of said paths is a series of two ormore nodes connected by links on which there are wavelengths at theservice level of that path.
 37. A machine-readable medium that providesinstructions that, if executed by a processor, will cause said processorto perform operations comprising: for each link to an adjacent node of awavelength division multiplexing optical network, classifyingwavelengths on that link according to a set of one or more service levelparameters for each of a plurality of service levels; for each of saidplurality of service levels, instantiate a service level topologystructure; and responsive to receiving information regardingconnectivity at each of said plurality of service levels to other accessnodes in said optical network, adding such information to said servicelevel topology structure for that service level.
 38. Themachine-readable medium of claim 37, wherein said classifying is basedon one or more of bandwidth, bit error rate, optical signal to noiseration, peak noise level, and re-routing priority.
 39. Themachine-readable medium of claim 37, the operations further comprising:for each link to an adjacent node, tracking said wavelengths byoperating a link management protocol.
 40. The machine-readable medium ofclaim 37, wherein said classifying includes comparing parameters of eachof the wavelengths to the sets of service level parameters.
 41. Themachine-readable medium of claim 37, wherein said adding includes, foreach of said service level topology structures, storing paths to thoseof other access nodes of said optical network that can be reached withthose of said wavelengths that qualify for the service level of thatservice level topology structure.
 42. The machine-readable medium ofclaim 41, wherein each of said paths is a series of two or more nodesconnected by links on which there are wavelengths at the service levelof that path.
 43. A method comprising: receiving a request for acommunication path starting at a source node in an wavelength divisionmultiplexing optical network; selecting a first of a plurality ofservice level, wherein different wavelengths on at least certain linksof said optical network qualifying for different ones of said pluralityof service levels forms a different service level topology for each ofsaid plurality of service levels for each access node of said opticalnetwork; selecting a path and a wavelength on said path using a databasethat stores, for each of the plurality of service levels, arepresentation of available paths from the source node to other accessnodes in said optical network, wherein each path is a series of two ormore nodes connected by links having a set of one or more wavelengths atthe same service level; and causing allocation of the selectedwavelength in the series of nodes of the selected path.
 44. The methodof claim 43, wherein said communication path is a lightpath.
 45. Themethod of claim 43, wherein said communication path is an opticalcircuit.
 46. The method of claim 43, wherein said selecting said pathand said allocation is performed in real time.
 47. The method of claim43, wherein the database stores a separate service level topologystructure for each of said service level topologies of said source node.48. The method of claim 47, wherein the database includes the availablewavelengths and the status as either allocated or unallocated.
 49. Themethod of claim 43, wherein said database stores, for each of theplurality of service levels, a representation of available conversionfree paths from the source node to other access nodes in said opticalnetwork.
 50. A machine-readable medium that provides instructions that,if executed by a processor, will cause said processor to performoperations comprising: responsive to receiving a request for acommunication path starting at a source node in an wavelength divisionmultiplexing optical network, selecting a first of a plurality ofservice level, wherein different wavelengths on at least certain linksof said optical network qualifying for different ones of said pluralityof service levels forms a different service level topology for each ofsaid plurality of service levels for each access node of said opticalnetwork; selecting a path and a wavelength on said path using a databasethat stores, for each of the plurality of service levels, arepresentation of available paths from the source node to other accessnodes in said optical network, wherein each path is a series of two ormore nodes connected by links having a set of one or more wavelengths atthe same service level; and causing allocation of the selectedwavelength in the series of nodes of the selected path.
 51. Themachine-readable medium of claim 50, wherein said communication path isa lightpath.
 52. The machine-readable medium of claim 50, wherein saidcommunication path is an optical circuit.
 53. The machine-readablemedium of claim 50, wherein said selecting said path and said allocationis performed in real time.
 54. The machine-readable medium of claim 50,wherein the database stores a separate service level topology structurefor each of said service level topologies of said source node.
 55. Themachine-readable medium of claim 54, wherein the database includes theavailable wavelengths and the status as either allocated or unallocated.56. The machine-readable medium of claim 50, wherein said databasestores, for each of the plurality of service levels, a representation ofavailable conversion free paths from the source node to other accessnodes in said optical network.
 57. A method comprising: receiving arequest to change a service provisioned with a communication pathestablished in a wavelength division multiplexing optical network at oneof a plurality of service levels to a different one of said plurality ofservice levels, wherein different wavelengths on at least certain linksof said optical network qualifying for different ones of said pluralityof service levels forms a different service level topology for each ofsaid plurality of service levels for each access node of said opticalnetwork; selecting a path and a wavelength on said path using a databasethat stores, for each of the plurality of service levels, arepresentation of available paths from a source node of saidcommunication path to other access nodes in said optical network,wherein each path is a series of two or more nodes connected by linkshaving a set of one or more wavelengths at the same service level;causing allocation of the selected wavelength in the series of nodes ofthe selected path to form a new communication path; and transitioningsaid service to the new communication path.
 58. The method of claim 57,wherein said communication path is a lightpath.
 59. The method of claim57, wherein said communication path is an optical circuit.
 60. Themethod of claim 57, wherein said selecting said path and said allocationis performed in real time.
 61. The method of claim 57, wherein thedatabase stores a separate service level topology structure for each ofsaid service level topologies of said source node.
 62. The method ofclaim 57, wherein said database stores, for each of the plurality ofservice levels, a representation of available conversion free paths fromthe source node of said communication path to other access nodes in saidoptical network.
 63. The method of claim 57, wherein said transitioningincludes: moving traffic from the previous communication path to the newcommunication path; and deallocating the previous communication path.64. A machine-readable medium that provides instructions that, ifexecuted by a processor, will cause said processor to perform operationscomprising: responsive to receiving a request to change a serviceprovisioned with a communication path established in a wavelengthdivision multiplexing optical network at one of a plurality of servicelevels to a different one of said plurality of service levels, selectinga path and a wavelength on said path using a database that stores, foreach of the plurality of service levels, a representation of availablepaths from a source node of said communication path to other accessnodes in said optical network, wherein different wavelengths on at leastcertain links of said optical network qualifying for different ones ofsaid plurality of service levels forms a different service leveltopology for each of said plurality of service levels for each accessnode of said optical network; wherein each path is a series of two ormore nodes connected by links having a set of one or more wavelengths atthe same service level; causing allocation of the selected wavelength inthe series of nodes of the selected path to form a new communicationpath; and transitioning said service to the new communication path. 65.The machine-readable medium of claim 64, wherein said communication pathis a lightpath.
 66. The machine-readable medium of claim 64, whereinsaid communication path is an optical circuit.
 67. The machine-readablemedium of claim 64, wherein said selecting said path and said allocationis performed in real time.
 68. The machine-readable medium of claim 64,wherein the database stores a separate service level topology structurefor each of said service level topologies of said source node.
 69. Themachine-readable medium of claim 64, wherein said database stores, foreach of the plurality of service levels, a representation of availableconversion free paths from the source node of said communication path toother access nodes in said optical network.
 70. The machine-readablemedium of claim 64, wherein said transitioning includes: moving trafficfrom the previous communication path to the new communication path; anddeallocating the previous communication path.
 71. A machine-readablemedium having stored thereon data comprising: a service levelconnectivity database for an access node of a wave division multiplexingoptical network, wherein each link of said optical network includes aset of zero or more lamdas for each of a plurality of service levels,each of said plurality of service levels includes a set of zero of morepossible end to end paths comprised of a series of one or more linksthat include one or more lamdas of that service level, said servicelevel connectivity database including, for each of the possible end toend paths that end with said access node, data representing, the seriesof links of that path; and the lamdas of that path.
 72. Themachine-readable medium of claim 71, further comprising: a link statedatabase including a link state structure for each node of said opticalnetwork adjacent said access node, each of said link state structuresincluding the set of zero lamdas for each of the plurality of servicelevels.
 73. The machine-readable medium of claim 71, wherein the servicelevel connectivity database includes a separate service level topologystructure for each of said plurality of service levels, each of saidplurality of service level topology structures storing the data for eachof the possible end to end paths of that service level that end withsaid access node.
 74. The machine-readable medium of claim 73, whereineach of said service level topology structures is a table.
 75. Themachine-readable medium of claim 73, wherein each of said service leveltopology structures is a tree.